Estimating the mirror seeing for a large optical telescope with a numerical method

摘要

It is widely accepted that mirror seeing is caused by turbulent fluctuations in the index of air refraction in the vicinity of a telescope mirror.Computational Fluid Dynamics (CFD) is a useful tool to evaluate the effects of mirror seeing.In this paper,we present a numerical method to estimate the mirror seeing for a large optical telescope (～ 4 m) in cases of natural convection with the ANSYS ICEPAK software.We get the FWHM of the image for different inclination angles (i) of the mirror and different temperature differences (△T) between the mirror and ambient air.Our results show that the mirror seeing depends very weakly on i,which agrees with observational data from the Canada-FranceHawaii Telescope.The numerical model can be used to estimate mirror seeing in the case of natural convection although with some limitations.We can determine △T for thermal control of the primary mirror according to the simulation,empirical data and site seeing.